Analyzers, particularly those involved with wet assays, conventionally require a washing station with a wash head to wash one or more containers used to carry out reactions. For example, in the Amerlite washer Model ZLE 202, a wash head is moved up and down into each of a series of containers arrayed on a moving platform, to aspirate out the incubated contents of each container and to wash the container several times. Because the wash head can use a solution of salts for the washing, it cannot be moved to a "home" position that exposes the head to the atmosphere. Otherwise, it is likely the head will crust over. Instead, it is commonly moved automatically into a soak reservoir to keep from drying out.
The problem with such an arrangement is that such varied positions for the wash head make it difficult to keep the movement of the head from deviating from a simple linear motion, e.g., down and up into and out of containers placed underneath the head. Although the soak reservoir can be just another position in the array of sample containers, the problem is that the contents of the soak reservoir need to be substantially larger than that of the sample containers, to avoid drying out the reservoir itself by evaporation. Furthermore, since the samples have to be removed after washing, such removal would also remove the soak reservoir.
On the other hand, it is more convenient to keep the motion of the wash head linear, if somehow the above-noted problems can be avoided.
Some attempts have been made in prior art analyzers to keep aspirators from departing from a linear up-and-down motion when they have to be cleaned (as opposed to being placed in a soak reservoir). However, typically the cleaning head undergoes a very complex disassembly and reassembly to move it away and back into alignment with the linear path of the aspirator. An example is shown in U.S. Pat. No. 4,820,497, which splits apart the cleaning head during its movement away. Such a construction is, of course, useless in the case of a soak reservoir that has to maintain a body of liquid.